Carbon Dioxide Transport and Sorption Behavior in Confined Coal Cores for Enhanced Coalbed Methane and CO2 Sequestration

Abstract

Measurements of sorption isotherms and transport properties of CO 2 in coal cores are important for designing enhanced coalbed methane/CO 2 sequestration field projects. Sorption isotherms measured in the lab can provide the upper limit on the amount of CO 2 that might be sorbed in these projects.Because sequestration sites will most likely be in unmineable coals, many of the coals will be deep and under considerable lithostatic and hydrostatic pressures. These lithostatic pressures may significantly reduce the sorption capacities and/or transport rates. Consequently, we have studied apparent sorption and diffusion in a coal core under confining pressure. A core from the important bituminous coal Pittsburgh #8 was kept under a constant, three-dimensional external stress; the sample was scanned by X-ray computer tomography (CT) before, then while it sorbed, CO 2 . Increases in sample density due to sorption were calculated from the CT images. Moreover, density distributions for small volume elements inside the core were calculated and analyzed. Qualitatively, the computerized tomography showed that gas sorption advanced at different rates in different regions of the core, and that diffusion and sorption progressed slowly. The amounts of CO 2 sorbed were plotted vs. position (at fixed times) and vs. time (for various locations in the sample). The resulting sorption isotherms were compared to isotherms obtained from powdered coal from the same Pittsburgh #8 extended sample.The results showed that for this single coal at specified times, the apparent sorption isotherms were dependent on position of the volume element in the core and the distance from the CO 2 source. Also, the calculated isotherms showed that less CO 2 was sorbed than by a powdered (and unconfined) sample of the coal. Changes in density distributions during the experiment were also observed. After desorption, the density distribution of calculated volume elements differed from the initial distribution, suggesting hysteresis and a possible rearrangement of coal structure due to CO 2 sorption.

Implementing Simulation and Artificial Intelligence Tools To Optimize the Performance of the CO2 Sequestration in Coalbed Methane Reservoirs

“…[1] There are two important parameters to consider when evaluating future CO2 sequestration in CBM reservoirs: the amount of gas that the reservoir can store, and, the potential to transport large quantities throughout the reservoir. [2] The increase in greenhouse gases in the atmosphere is one of the most important environmental issues, which leads into global warming. Increasing the efficiency of power plants or switching from coal to much more environmentally friendly fossil fuels such as natural gas are among the ways to reduce the carbon dioxide emission.…”